stretched movie when masking?
Unfortunately the movie clip editor doesn't seem to have a way to deal with non-square pixels. So your mask is getting created using a frame that is 1440x1080 pixels.

When you bring that into the VSE editor it is stretching that frame to fill a 1920x1080 canvas (as determined by your render settings)

So there are three choices:

1. (The one I would use because I dislike the VSE so much) Use the compositor.

Setup your mask at a fixed size of 1440x1080 and composite using the Alpha Over node.



2. If you must use the VSE. Change your render settings to 1440x1080 with a pixel aspect ratio of X:1.33 Y:1



or 

3. Keep your settings the way they are now and deform the mask strip on the VSE:
In VSE you select your mask strip and add a Effect Strip->Transform strip. Then change the settings to use 0.75 on the Y scale to have the mask match the aspect ratio of the original footage.